- Bourlat, Sarah, et al.
Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida
Ingår i: Nature. ; 444:7115, s. 85-88
- Deuterostomes comprise vertebrates, the related invertebrate chordates (tunicates and cephalochordates) and three other inver- tebrate taxa: hemichordates, echinoderms and Xenoturbella1. The relationships between invertebrate and vertebrate deuterostomes are clearly important for understanding our own distant origins. Recent phylogenetic studies of chordate classes and a sea urchin have indicated that urochordates might be the closest inverte- brate sister group of vertebrates, rather than cephalochordates, as traditionally believed2–5. More remarkable is the suggestion that cephalochordates are closer to echinoderms than to vertebrates and urochordates, meaning that chordates are paraphyletic2. To study the relationships among all deuterostome groups, we have assembled an alignment of more than 35,000 homologous amino acids, including new data from a hemichordate, starfish and Xenoturbella. We have also sequenced the mitochondrial genome of Xenoturbella. We support the clades Olfactores (urochordates and vertebrates) and Ambulacraria (hemichordates and echino- derms6). Analyses using our new data, however, do not support a cephalochordate and echinoderm grouping and we conclude that chordates are monophyletic. Finally, nuclear and mitochondrial data place Xenoturbella as the sister group of the two ambulacrar- ian phyla1. As such, Xenoturbella is shown to be an independent phylum, Xenoturbellida, bringing the number of living deutero- stome phyla to four.